This invention relates to semiconductor packaging and, particularly, to lead frame packaging such as QFN (“Quad Flat No-lead”) packaging.
A conventional QFN lead frame package includes a lead frame consisting of a centrally situated die paddle and peripheral leads, and a die attached to, and electrically connected with, the lead frame; and a molding or in capsulation that seals all of the parts of the die-and-lead frame assembly, and leaves land portions of the leads exposed for second-level interconnection of the package to circuitry in the environment of use, such as circuitry on a printed circuit board.
The die in a lead frame package may be affixed to the lead frame by attaching the backside of the die to the die paddle using a die attach adhesive; and in such an arrangement, where the active side of the die faces away from the lead frame (that is, the active site of the die faces “upward”), electrical interconnection of the die with the lead frame can be made by way of wire bonds between interconnect pads on the die and bond sites on the leads.
Or, the die in a lead frame package may be a so-called flip chip die, which is situated in the package with the active side toward the lead frame, and he is attached and electrically connected to the leads by flip chip interconnections between peripheral pads on the die and bond sites on the leads. In a flip chip lead frame package of this type, there is no direct mechanical or electrical connection between the die and the die paddle.
In a conventional flip chip QFN lead frame package, therefore, electrical connections between the die and the lead frame are made only by way of connection of peripheral die pads with the leads. In many die, interconnect pads are situated in a central portion of the die, and particularly die pads for power and ground interconnection may be situated in a center portion of the die. Such die cannot be mounted in a conventional flip chip QFN package, and some proportion of the peripheral die pads must be dedicated to ground or power connection.
Also, in a conventional flip chip QFN package, the active side of the die is separated from the die paddle and, accordingly, if heat generated at the active site of the die is to pass out of the package by way of the die paddle, the heat must pass through a layer of encapsulation or molding between the die and the die paddle.